1. Field of the Invention
This invention relates generally to a mechanical press drive for moving the upper platen of a press up and down.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Presses used for hemming operations are well known in the art. Such a press will exert forces exceeding 200,000 pounds and will typically use a hydraulic cylinder to raise and lower an upper platen and die assembly of the press. Increasingly, facilities that use presses are desirous of replacing their hydraulic drives with mechanical drives that incorporate ballscrews. A mechanical drive has the advantage of being more environmentally friendly than a hydraulic drive because mechanical drives are not prone to hydraulic fluid leaks and don""t present hydraulic fluid disposal problems. Additionally, a mechanical drive consumes less energy than a hydraulic drive, and is quieter in operation. Finally, a mechanical drive is more reliable and thus experiences less down time, and can be designed with positive positioning and positive position holding features.
A ballscrew can be incorporated into a mechanical drive for a press. Ballscrew driven presses have disadvantages that have prevented wider use of ballscrew driven presses. The interface between the shaft or screw portion of a ballscrew apparatus and its ballscrew nut is sensitive to offset or moment loads, and such loads can cause a ballscrew drive to fail prematurely. As a result, if a press platen is not balanced, it can present an offset load to the ballscrew that can cause it to fail. Although care can be taken to ensure that offset loads or moments are minimized through the design of the press and of the tooling, it is impossible to guarantee that the press will never be subjected to unbalanced loads by the end user. Another source of an unbalanced load is the possibility of a tool or other foreign object being accidentally left on the lower die in an open press, that, when the press is cycled to a closed position, will exert a large unbalanced load on the upper die assembly or platen. Accordingly, it would be desirable to provide a mechanical press drive that incorporates a ballscrew apparatus that""s not susceptible to damage when unbalanced loads are applied to the platen.
The invention is a mechanical press drive for moving the upper platen of a press up and down. The press drive includes a ballscrew apparatus comprising a nut and a screw threadedly engaging the nut. The mechanical press drive also includes a first coupling connected to the screw and configured to connect the screw to one of a movable platen of a press or a stationary member of the press. A second coupling is connected to the nut and is configured to connect the nut to the other of the platen and the stationary member of the press. A drive motor is operably connected to one of the nut and screw and is configured to relatively rotate the nut and screw and impart reciprocal motion to the movable platen.
The two couplings are configured to cooperatively isolate the ballscrew apparatus from offset and moment loading that may occur during press operation. The couplings isolate the ballscrew apparatus while transmitting driving torque about the longitudinal axis of the ballscrew and forces along the longitudinal axis to the platen. Preferably, the couplings are gimbals.
Objects, features and advantages of this invention include providing a mechanical press drive that uses a ballscrew apparatus to raise and lower a movable platen and that isolates the ballscrew apparatus from offset or moment loads, and providing such a mechanical press drive that includes gimbals mounted on screw and nut portions of the ballscrew apparatus, respectively, to isolate the ballscrew apparatus from offset or moment loads, and is rugged, durable, economical and in service has a long useful life.